>> I
>> found that running the same source code on these OS, with the same
>> versions of of gcc and open-mpi installed on them, gives different
>> results than Fedora and Ubuntu after a few hundred iterations. The first
>> few hundered iterations are exactly similar to that of Fedora and
>> Ubuntu but then it starts giving different results.

> Are you also using the same hardware? Different hardware platforms may
> exhibit different rounding behaviour. After some dependent interations
> such effects might indeed sum up and yield different results. The issue
> is called numeric (in)stability and is not specifically related to openmpi.

Yes I use different machines such as

machine 1 uses AMD Opterons. (Fedora)

machine 2 and 3 use Intel Xeons. (CentOS)

machine 4 uses slightly older Intel Xeons. (Debian)

Only machine 1 gives correct results. While CentOS and Debian results are same but are wrong and different from those of machine 1.

Cheers,

Asad

"Statistical thinking will one day be as necessary for efficient citizenship as the ability to read and write." - H.G. Wells